BACKGROUND AND OBJECTIVES: Coronary artery
disease (CAD) patients are at greater perioperative morbidity and mortality
risk during non-cardiac surgery. Specific laboratory tests are important adjuncts
to clinical tests and should be one of the tools for evaluating and preparing
those patients. This review aims at establishing preoperative procedures to
minimize peri and postoperative morbidity and mortality in CAD patients.CONTENTS: Characteristics of stable and unstable chest anginas are presented,
along with clinical and functional classification criteria, diagnosis, clinical-surgical
therapy and major cardiologic laboratory tests. In addition, types of angina
are correlated to clinical procedures in order to propose a preoperative algorithm.CONCLUSIONS: All CAD patients being considered for non-cardiac surgery
should be carefully evaluated. Patients at high-risk require effective clinical
control. For clinically stable patients, in the intermediate-risk group, functional
non-invasive tests are recommended. The use of beta-blockers should be considered
for all coronary patients.

Coronary failure or disease is
the unbalance between myocardial oxygen supply and demand and may cause ischemia
and heart cell necrosis. Coronary changes are major causes of cardiomyopathies
and death among adults and are responsible for approximately 40% of all deaths
of individuals above 60 years of age. Common etiology is arteriosclerosis, the
incidence of which increases with age. In males, it evolves very rapidly between
30 and 50 years of age, time when it starts to more gradually progress and reaches
its peak at 60 or 65 years of age. In females, atheromatosis onset is late and
coincides with menopause. In individuals below 40 years of age, damages are
more localized and affect one artery. In elderly, however, damages are in general
diffuse and may affect many branches. Coronary disease patients submitted to
surgeries are not an infrequent event. It is estimated that 12% of patients
submitted to non-cardiac surgery present or are at risk for coronary disease1,2. Undesirable events, fatal or not, depend on location, number
of vessels affected and the degree of obstructive injuries and of the functional
importance of the affected vessel. Those patients are at increased risk for
peri and postoperative morbidity and mortality and should be evaluated and prepared
by a multidisciplinary team, including the anesthesiologist, whose participation
is paramount for a successful procedure.

DIAGNOSIS

Clinical diagnosis is often based
on ECG, the most important findings of which are changes in the ST segment3.
However, a normal ECG is frequently seen in patients with chronic artery disease.
Subsequent lab tests aim at: a) explaining situations with inconclusive results;
b) functionally classifying chronic artery disease patients; and c) defining
therapeutic goals.

CLASSIFICATION

Coronary patients are classified according to
clinical and functional characteristics. The clinical classification establishes
two groups: stable and unstable chronic angina. The latter has several clinical
variances (recent angina, rapidly progressive angina, subentrying angina, intermediate
syndrome and post recent infarction angina). Stable chronic angina is characterized
by retro-sternal pain episodes in grasp, triggered by physical or emotional
stress. Pain lasts from two to ten minutes and disappears with rest or sublingual
nitrates. Unstable angina is a clinical status with imminent risk for acute
myocardial infarction. Crises may occur at rest or minimum efforts, seem to
be related to coronary artery tone and do not disappear with normal therapy.
Prinzmetal angina is in general considered a separate disease. It is rare and
in general severe with 2/3 of patients presenting significant proximal coronary
injuries4. So Prinzmetal patients should be treated as unstable
angina patients. The functional classification relates to physical activities
coronary patients are entitled to perform. Patients may belong to functional
classes I, II, III or IV (Chart I),
according to their functional capacity5,6. This variable is estimated
in metabolic equivalents (METs) where 1 MET is equivalent to the consumption
of 3.5 ml O2.kg-1.min-1 or the consumption
of a 70 kg person at rest and in the supine position (Chart
II). Functional capacity is considered excellent if higher than 7 METs,
moderate if between 4 and 7 METs and poor when lower than 4 METs7,8.

TREATMENT

The initial treatment is clinical
with nitrates, beta-blockers and calcium channel blockers. Anti platelet aggregation
drugs should be administered to all angina patients. Once the diagnosis is determined,
chronic artery disease patients should be immediately treated and those with
unstable angina or stable angina functional class III or IV should be referred
to cinecoronariography9. Patients with stable angina functional
class I or II must have their functional capacity confirmed. Ergonometric tests
are excellent for such end10. Those with poor functional capacity
should be further evaluated by cinecoronariography7-9. On the other
hand, chronic artery disease patients, with moderate or excellent functional
capacity, do not need additional evaluations; just follow up and clinical therapy7,8.

Cinecoronariography locates and
defines coronary injuries, in addition to determining the therapeutic approach.
Coronary angioplasty (with or without stent) is indicated for obstructive injuries
with stenosis of the vessel's lumen diameter higher than 70% (flow limiting
injuries), especially those of types A and B1. These obstructive
injuries are small (< 10 mm), concentric, easily accessible, with non angulated
segments, smooth contours, few or no calcification and lack of ostial injury.
Injuries B2 and C are more complex, eccentric and tortuous11.
Even so, they may today be corrected by angioplasty (stent) performed by an
experienced surgeon although with a higher procedure-related risk. Flow limiting
injuries in a coronary branch is an absolute indication for surgical myocardial
revascularization. Similarly, coronary ostium injuries are also indications
for revascularization surgeries, although in special situations and with experienced
professionals angioplasty may be attempted, especially in emergency situations11. Flow limiting multiartery injuries justify a thorough clinical
discussion with the participation of the hemodynamics specialist and the cardiac
surgeon, due to the possibility of only being corrected by myocardial revascularization.

PREOPERATIVE EVALUATION AND
PREPARATION

The surgical risk of non cardiac surgeries is
classified in high, intermediate and low risk, according to the possibility
of death and non fatal myocardial infarction. If the incidence of such events
is above 5%, surgeries are considered of high risk; if between 1% and 5%, they
are considered of moderate risk; and if below 1% they are considered of low
risk (Chart III)7,8.

The incidence of acute myocardial
infarction (AMI) after non cardiac surgeries in the non cardiac population varies
from 0.1% to 0.2%. This incidence significantly increases among coronary artery
disease patients and varies from 2% to 17%12. Half of the ischemic
events occur on the day of the surgery, but the incidence peak is seen on the
third day1,2. Perioperative mortality is also higher in cardiac
patients. On the other hand, those submitted to previous successful revascularization
have a postoperative mortality equivalent to individuals without coronary disease13. Surgery and anesthesia cause a circulatory overload to which
the ill heart is more exposed than the healthy heart14. So, a careful
clinical evaluation, supported by additional preoperative tests, is a major
foundation for an accurate evaluation and may decrease surgical morbi-mortality
of cardiac patients, thus assuring the success of the procedure.

The preoperative evaluation of
clinically stable coronary disease patients scheduled for non cardiac surgery
consists initially of a detailed clinical exam and conventional ECG, which allow
for determining associated co-morbidity, stratifying the surgical risk, adopting
different approaches and intervening, when necessary, before the non cardiac
surgery.

The additional preoperative investigation of
cardiac patients is based on the clinical form of their disease and on the type
of surgical procedure they will be submitted to. So, patients with unstable
or stable functional class III or IV angina, recent myocardial infarction (up
to one month) or those with evidences of residual ischemia are considered at
high risk (Chart IV) and should be
evaluated by cinecoronariography and possible angioplasty or myocardial revascularization
before the non cardiac surgery7,8. On the other hand, patients with
stable angina functional class I or II are at intermediate risk and should be
classified according to their functional capacity. It is worth mentioning that
in some situations it is not possible to clinically evaluate the functional
capacity. In those cases, it should be determined by a stress test, which in
some cases may be impossible to apply. So, another non-invasive test should
be considered to estimate preoperative risk and management.

Low functional capacity has been considered a
predictive factor for surgical risk in non cardiac surgeries. So, patients at
intermediate risk with low functional capacity should be submitted to other
non-invasive cardiologic tests before being sent to surgery, regardless of the
type of surgery7,8. Similarly, those with moderate or excellent
functional capacity and scheduled for high risk procedures should be submitted
to the same tests to classify the risk. Such tests, however, are unnecessary
if the surgery is of low or intermediate risk. When non-invasive tests reveal
patients at high surgical risk, cinecoronariography should be considered7,8.
When the same tests reveal low or moderate risk, patients should be sent to
surgery. Chart V summarizes in an
algorhythm a proposal to preoperatively evaluate coronary disease patients.

As to drug treatment, there are
no doubts that the surgical stress promotes an increase in catecholamines, which
may cause adverse cardiac effects. So, patients are more vulnerable to arrhythmias
and arteriosclerotic plate rupture. That is why perioperative beta-blockers
have been proposed in non cardiac surgeries for chronic artery disease patients.
Those agents decrease the incidence of ischemia and myocardial infarction, not
only in the perioperative period, but also in the long run. Based on those evidences,
b-antagonists should be routinely used in the perioperative
period of cardiac patients except when counterindicated15.

NON-INVASIVE AND SEMI-INVASIVE
CARDIOLOGIC TESTS

Most common non-invasive cardiologic
tests are bidimensional echocardiography, ergonometric test, stress echocardiography
with dobutamine, myocardial scintigraphy with dipyridamole and holter. Transesophageal
doppler echo-cardiography is a semi-invasive method very useful to evaluate
coronary patients.

Bidimensional echocardiography
- the echocardiography lab allows for the division of the left ventricle
in several segments (11, 13 or 16) and for the evaluation of global and regional
functions, end systolic volume and ejection fraction. In the vast majority of
coronary disease patients, it is possible to determine changes in segmental
contractility16. The best way to detect myocardial ischemia is through
the abnormal movement of the ischemic segment (decrease of segmental systolic
inspissator in the region of the affected wall). The involvement of up to two
segments should be analyzed together with ventricular and functional capacity.
On the other hand, changes in three or more segments in different regions characterize
a patient at high surgical risk. If there is no segmental contractility changes
but there is a clinical suspicion of myocardial ischemia, patient should be
submitted to ergometric test or stress echocardiography. End systolic volume
is of paramount importance to evaluate ejection efficiency of the left ventricle
and is the major determinant of survivors after myocardial infarction. End systolic
volume lower than or equal to 34 ml.m2 correlates to a lower death
rate. Ejection fraction lower than 50% with high end systolic volume is a predictive
factor for future cardiac events17,18.

Ergometric test - evaluates
cardiovascular overload imposed by physical exercise and functional capacity.
It does not consider, however, the effects of psychological stress which affects
factors determining myocardial oxygen consumption. The ergometric test applied
to chronic multiartery disease patients is approximately 90% sensitive19.
Patients with functional capacity below 4 METs and low physical activity level-induced
myocardial ischemia (ST segment under-unlevelled) are at high peri and postoperative
risk. On the other hand, ischemic patients with functional capacity above 7
METs are considered at low cardiac risk10.

Stress echocardiography with
dobutamine - very useful method to evaluate patients with diseases (neurological,
orthopedic, etc.) which prevent the ergometric test. Followed by transthoracic
echocardiography at rest, the stress echocardiography with dobutamine may induce
myocardial ischemia and has shown to be better than the sub-maximal ergometric
test to diagnose multiartery disease patients20,21. A low butamine
dose (5 µg.kg-1.min-1) may detect feasible ischemic
muscle and myocardial involvement. When the technical quality of the transthoracic
stress echocar- diography is limited, the transesophageal method with stress
may replace it, giving important information about patients with triartery involvement22. The normal test has a negative predictive value of 93% to 100%
and segmental contraction abnormalities have a positive predictive value of
7% to 50% and may be considered as risk factors for peri and postoperative cardiac
events23. Abnormal contractions in three or more segments
of ischemics different regions indicate patients at high risk for peri or postoperative
cardiac events.

Myocardial scyntigraphy with
dipyridamole - thalium or sestamibi scintigraphy with pharmacological stress
induced by dipyridamole may show the existence of reversible or non reversible
ischemias (previous infarction) with high sensitivity (93%) although the low
specificity of the method (62%). A fixed ischemia in 1 or 2 segments should
be evaluated together with the ventricular function. However, 3 or more ischemic
segments characterize high risk patients. Some authors have shown defects of
thalium redistribution and perioperative ischemia. Low specificity and high
cost limit its use24.

Holter - the long duration
electrocardiography may detect transient ischemic episodes characterized by
ST segment under-unlevelling in severe cardiac patients who never referred angina
pain even during a myocardial infarction4. This method may be useful,
especially in diabetes type 2 patients who have a higher incidence of silent
ischemic events; however, there are many false-positive results in normal individuals25. There are certain limitations of the method for patients with
abnormal ECG at rest. Per se, this exam is not enough to refer patients to cinecoronariography.

Transesophageal doppler echocardiography
- this semi-invasive method is very useful to evaluate blood flow velocity
in coronary circulation and coronary reserve flow (CRF) in the anterior descending
aorta and the coronary sinus. The baseline flow velocity is obtained during
maximum hyperemia induced by venous adenosine for 4 minutes. CAD patients with
moderate functional capacity and scheduled for high risk surgeries should be
submitted to transesophageal echocardiography. When CRF is higher than 2, severe
coronary injuries may be ruled out, and when lower than 2, obstructive injuries
are considered significant and patients are at high risk26,27. Some
countries adopt this method as a perioperative routine for high risk surgeries.
This monitoring explains in a sensitive and continuous way, global and segmental
functions of the left ventricle without interfering with the surgical field.
Using this method one may obtain the perioperative etiology of an acute hypotension
or the onset of a left ventricular myocardial ischemia before electro- cardiographic
changes are seen, faster, safer and more reliable way than when using
pulmonar artery catheterization28,29.

All chronic artery disease patients
scheduled for non cardiac surgeries must be carefully evaluated. Those at high
risk need a strict clinical control. Elective procedures should be postponed
in adverse clinical situations where patients are not compensated. For clinically
stable patients (most of them functional class I or II) and considered of moderate
risk, non-invasive functional tests are recommended. b-blockers
should be considered for all coronary disease patients.